Flywheel systems and flywheel bearing modules

ABSTRACT

A flywheel system includes a fixture providing a base and a stator, rotor having a cavity to receive the stator, a generator/motor module having a plurality of permanent magnets mechanically coupled to the rotor and an active magnetic bearing module. The active magnetic bearing module includes a plurality of magnetizable elements mechanically coupled to or integrated in the rotor, and a plurality of electromagnets mechanically coupled to a shaft and configured to magnetically couple with the plurality of first magnetizable elements to actively stabilize the rotor relative to the fixture. The windings of the generator/motor module are arranged around the rotation axis of the rotor at a first distance from the rotation axis of the rotor, the electromagnets of the active magnetic bearing module are arranged around the rotation axis of the rotor at a second distance, and the first distance is greater than or equal to the second distance.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/682,331 filed Feb. 28, 2022, which is a continuation of U.S.patent application Ser. No. 16/758,298 filed Apr. 22, 2020, which is a35 U.S.C. § 371 filing of International Application No.PCT/DK2018/050265 filed Oct. 22, 2018, which claims the benefit ofpriority to U.S. Provisional Application No. 62/575,489, filed Oct. 22,2017, and Danish Patent Application No. PA 2018 00643 filed Sep. 26,2018, each of which is incorporated herein by reference in its entirety.

BACKGROUND

A flywheel system is a mechanical device that stores rotational energyin a mass. The amount of energy stored in the rotor is proportional tothe square of the rotor's rotational speed. The rotor may bemagnetically coupled with an electromagnetic generator stator to allowthe flywheel system to convert between rotational energy of the rotorand electrical energy. The generator stator may decelerate the rotor toproduce electrical energy from the rotational energy extracted from therotor, and the generator stator may receive electrical energy andconvert this electrical energy to rotational energy of the rotorresulting in acceleration of the rotor. Flywheel systems may be designedto have large energy storage capacity, and are further capable of bothdelivering and absorbing energy rapidly. Common uses of a flywheelsystem include (a) peak-shaving of the power output of another energysource such as a combustion generator stator, (b) energy storage, (c)backup power supply, and (d) rapid energy delivery.

Low-loss energy storage in a flywheel system requires that the rotorrotates with very little friction. Therefore, the rotor of ahigh-performance flywheel system typically is magnetically levitated.

SUMMARY

In an embodiment, a flywheel system includes a rotor configured torotate about a rotation axis. The flywheel system further includes afixture and an active magnetic bearing module for actively stabilizingthe rotor relative to the fixture. The active magnetic bearing moduleincludes a plurality of first magnetizable elements mechanically coupledto or integrated in the rotor, and a plurality of electromagnetsmechanically coupled to the fixture and configured to magneticallycouple with the plurality of first magnetizable elements to activelystabilize the rotor relative to the fixture. Each of the firstmagnetizable elements is farther than each of the electromagnets fromthe rotation axis.

Optionally, each of the first magnetizable elements is a soft magneticcomposite.

Optionally, the first magnetizable elements are arranged along a firstdiameter about the rotation axis, the electromagnets being arrangedalong a second diameter about the rotation axis, the first diameterbeing greater than the second diameter.

Optionally, in dimensions orthogonal to the rotation axis, theelectromagnets and the first magnetizable elements are away from eachother by a first radial gap, the first radial gap being in range between2 and 10 millimeters.

Optionally, extent, along the rotation axis, of the first magnetizableelements exceeding extent along the rotation axis, of theelectromagnets.

Optionally, the rotor forms a first void encircling the rotation axis,the plurality of first magnetizable elements being positioned at a firstsurface of the first void that encircles the rotation axis and faces therotation axis, each of the electromagnets being positioned in the firstvoid to magnetically couple with the first magnetizable elements acrossa portion of the first void.

Optionally, permanent magnets are mechanically coupled to or integratedin the rotor and positioned at a second surface of the first void thatencircles the rotation axis; and a generator stator is mechanicallycoupled to the fixture and positioned in the first void to magneticallycouple with the permanent magnets, so as to convert between rotationalenergy of the rotor and electric current in windings of the generatorstator.

Optionally, the fixture comprises an endplate positioned adjacent a topend or a bottom end of the rotor, the electromagnets and the generatorstator being attached to the endplate.

Optionally, the generator stator is between the electromagnets and theendplate, the second surface being closer than the first surface to theendplate.

Optionally, the electromagnets are between the generator stator and theendplate, the first surface being closer than the second surface to theendplate.

Optionally, the endplate forms a base adjacent the bottom-end, theflywheel system further comprises: first load bearing magnetsmechanically coupled to or integrated in the rotor at bottom surface ofrotor; second load bearing magnets, mechanically coupled to the base,for magnetically coupling with the first load bearing magnets tomagnetically levitate the rotor above the base.

Optionally, in the first void, there is at least one passive magneticbearing for stabilizing the rotor relative to the fixture if the activemagnetic bearing loses power, each passive magnetic bearing comprising:second permanent magnets mechanically coupled with the rotor; and thirdpermanent magnets mechanically coupled to the fixture and positioned inthe first void to magnetically couple with the second permanent magnets,so as to provide backup stabilization of the rotor relative to thefixture.

Optionally, the at least one passive magnetic bearing comprises aplurality of passive magnetic bearings located in different respectivepositions.

Optionally, in dimensions orthogonal to the rotation axis, theelectromagnets and the first magnetizable elements are apart from eachother by a first radial gap, and the generator stator and the permanentmagnets are apart from each of by a second radial gap that exceeds thefirst radial gap.

Optionally, each of the first surface and the second surface facing therotation axis, the first surface and the second surface are respectiveportions of a common cylindrical surface.

Optionally, each of the first surface and the second surface facing therotation axis, diameter of the first surface are different from diameterof the second surface.

Optionally, each of the first surface and the second surface facing therotation axis, the first void span across the rotation axis.

Optionally, the first void is a groove that encircles the rotation axisbut does not coincide with the rotation axis, the rotor further forms acentral void closer than the groove to the rotation axis, the flywheelsystem further comprising: permanent magnets are mechanically coupled toor integrated in the rotor and positioned at a second surface of thecentral void that faces and encircles the rotation axis; and a generatorstator is mechanically coupled to the fixture and positioned in thecentral void to magnetically couple with the permanent magnets, so as toconvert between rotational energy of the rotor and electric current inwindings of the generator stator.

Optionally, the fixture comprises an endplate positioned adjacent a topend or bottom end of the rotor, the electromagnets and the generatorstator being attached to the endplate.

Optionally, the endplate forms a base positioned adjacent the bottom endof the rotor, the flywheel system further comprising: first load bearingmagnets mechanically coupled to or integrated in the rotor at bottomsurface of rotor; and second load bearing magnets, mechanically coupledto the base, for magnetically coupling with the first load bearingmagnets to magnetically levitate the rotor above the base.

Optionally, in one or both of the groove and the central void, there isat least one passive magnetic bearing for stabilizing the rotor relativeto the fixture if the active magnetic bearing loses power, each passivemagnetic bearing comprising: second permanent magnets mechanicallycoupled to or integrated in the rotor; and third permanent magnetsmechanically coupled to the fixture and positioned in the groove or thecentral void to magnetically couple with the second permanent magnets,so as to provide backup stabilization of the rotor relative to thefixture.

Optionally, the at least one passive magnetic bearing comprises aplurality of passive magnetic bearings located in different respectivepositions.

Optionally, there is a power supply for powering the plurality ofelectromagnets to adjust position of the rotor relative to the fixture;and at least one sensor for sensing a movement characteristic of therotor relative to the fixture, the at least one sensor beingcommunicatively coupled with the power supply to enable adjustment ofthe position of the rotor relative to the fixture in response to themovement characteristic.

Optionally, there is at least one passive backup bearing includingsecond permanent magnets for stabilizing the rotor relative to thefixture if the power supply fails to provide power to one or more of theplurality of electromagnets.

In an embodiment, a bearing module for a flywheel system includes aplurality of first magnetizable elements arranged along a first diameterand configured to be mechanically coupled to a rotor of the flywheelsystem, and a plurality of electromagnets configured to be mechanicallycoupled to a fixture and magnetically couple with the first magnetizableelements to stabilize the rotor relative to the fixture. Theelectromagnets are bounded by a second diameter that is smaller than thefirst diameter to enable positioning of the electromagnets inside thefirst diameter.

Optionally, each of the first magnetizable elements is a soft magneticcomposite.

Optionally, there is at least one sensor for sensing a positioncharacteristic of the rotor relative to the fixture; and a power supply,communicatively coupled with the at least one sensor, for powering theelectromagnets to adjust position of the rotor relative to the fixturein response to the position characteristic.

Optionally, there is at least one passive magnetic bearing including (a)a plurality of first permanent magnets configured to be mechanicallycoupled to the rotor and (b) a plurality of second permanent magnetsconfigured to be mechanically coupled to the fixture and magneticallycouple with the first permanent magnets to stabilize the rotor relativeto the fixture if the power supply fails to provide power to theelectromagnets.

Optionally, there is a plurality of third permanent magnets arrangedalong a third diameter and configured to be mechanically coupled to therotor; and a generator stator for magnetically coupling with the thirdpermanent magnets, to convert between rotational energy of the rotor andelectric current in windings of the generator stator.

Optionally, the generator stator is bounded by a fourth diameter that issmaller than the third diameter to enable positioning of the generatorstator inside the third diameter.

Optionally, the electromagnets are mounted on the generator stator.

Optionally, there is first load bearing magnets configured to bemechanically coupled to the rotor; and second load bearing magnetsconfigured to be mechanically coupled to the fixture and magneticallycouple with the first load bearing magnets to magnetically levitate therotor above the second load bearing magnets.

In an embodiment, a bearing module is integrated with a generator. Theintegrated bearing module and generator are configured for use in aflywheel system and include a plurality of permanent magnets, agenerator stator, and an active magnetic bearing. The plurality ofpermanent magnets are arranged along a first diameter and configured tobe mechanically coupled to a rotor of the flywheel system. The generatorstator is configured to be mechanically coupled to a fixture. Thegenerator stator is bounded by a second diameter that is smaller thanthe first diameter to enable positioning of the generator stator insidethe first diameter to magnetically couple with the permanent magnets, soas to convert between rotational energy of the rotor and electriccurrent in windings of the generator stator. The active magnetic bearingincludes (a) a plurality of first magnetizable elements arranged along athird diameter and configured to be mechanically coupled to the rotor,and (b) a plurality of electromagnets arranged along a fourth diameterand configured to be mechanically coupled to the fixture andmagnetically couple with the first magnetizable elements. The thirddiameter is greater than the first diameter to enable positioning of thefirst magnetizable elements at greater distance than the permanentmagnets from rotation axis of the rotor. The fourth diameter is greaterthan the first diameter to enable positioning of the active magneticbearing at greater distance than the permanent magnets from the rotationaxis.

Optionally, each of the first magnetizable elements being a soft magnet.

Optionally, the fourth diameter is greater than the third diameter toenable positioning of the first magnetizable elements closer than theelectromagnets to the rotation axis.

Optionally, the fourth diameter is smaller than the third diameter toenable positioning of the first magnetizable elements farther than theelectromagnets from the rotation axis.

Optionally, there is an endplate that forms at least a portion of thefixture, the generator stator and the electromagnets being mounted onthe endplate.

Optionally, first load bearing magnets are configured to be mechanicallycoupled to the rotor; and second load bearing magnets configured to bemechanically coupled to the fixture and magnetically couple with thefirst load bearing magnets to magnetically levitate the rotor above thesecond load bearing magnets.

Optionally, there is at least one sensor for sensing a positioncharacteristic of the rotor relative to the fixture; and a power supply,communicatively coupled with the at least one sensor, for powering theelectromagnets to adjust position of the rotor relative to the fixturein response to the position characteristic.

Optionally, at least one passive magnetic bearing includes (a) aplurality of second permanent magnets configured to be mechanicallycoupled to the rotor and (b) a plurality of third permanent magnetsconfigured to be mechanically coupled to the fixture and magneticallycouple with the second permanent magnets to stabilize the rotor relativeto the fixture if the power supply fails to provide power to theelectromagnets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flywheel system in an exemplary use scenario,according to an embodiment.

FIG. 2 illustrates a flywheel system that includes an active magneticbearing to actively stabilize the rotor of the flywheel system relativeto the foundation of the flywheel system, according to an embodiment.

FIG. 3 schematically illustrates an active magnetic bearing module for aflywheel system, according to an embodiment.

FIG. 4 illustrates an active magnetic bearing for use in a flywheelsystem, according to an embodiment.

FIG. 5 illustrates a flywheel system having an active magnetic bearingpositioned in a void of the rotor, according to an embodiment.

FIG. 6 illustrates an alternate flywheel system implementing an activemagnetic bearing at a shaft of the flywheel system.

FIG. 7 illustrates a flywheel system having an active magnetic bearingthat is integrated with a generator of the flywheel system, according toan embodiment.

FIG. 8 illustrates a bearing module having both an active magneticbearing and a passive magnetic backup bearing, according to anembodiment.

FIG. 9 illustrates a flywheel system that has an active magnetic bearingintegrated with a generator of the flywheel system and further includesone or more passive magnetic backup bearings, according to anembodiment.

FIG. 10 illustrates another flywheel system having an active magneticbearing that is integrated with a generator of the flywheel system,according to an embodiment.

FIG. 11 illustrates a flywheel system having an active magnetic bearingthat is integrated with a generator of the flywheel system with both theactive magnetic bearing and the generator being mounted above a top endof the rotor of the flywheel system, according to an embodiment.

FIG. 12 illustrates a flywheel system including a generator and anactive magnetic bearing positioned at greater radii than the generator,according to an embodiment.

FIG. 13 illustrates another flywheel system including a generator and anactive magnetic bearing positioned at greater radii than the generator,according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Flywheel systems are being considered for use in offshore or onshoreenvironments not connected to a conventional electrical grid but insteadrelying on a so-called micro grid. In these environments, flywheelsystems may serve as a source of energy and, for example, provide powerfunctionalities such as peak-shaving or frequency control. In addition,flywheel systems may serve to rapidly meet a high, short-term powerdemand. When implemented in environments that are potentially unstable,such as onboard a drillship, a semisubmersible drilling platform, oranother marine vessel, the flywheel system is subject to substantialforces which can affect both the performance and lifetime of theflywheel system.

Disclosed herein are active magnetic bearings configured to activelystabilize the rotor of a flywheel system relative to the foundation ofthe flywheel system. These active magnetic bearings enableimplementation of flywheel systems in both offshore environments andunstable onshore environments such as locations subject to earthquakes.Herein, an “active magnetic bearing” refers to a bearing that isadjustable based upon an input signal. An active magnetic bearing may becoupled with one or more sensors in a feedback loop.

FIG. 1 illustrates one flywheel system 100 in an exemplary use scenarioincluding a rotor 110 and a fixture 120 that supports rotor 110. Rotor110 is configured to rotate about a rotation axis 190, as indicated byarrow 192 or in the direction opposite arrow 192. Fixture 120 couplesrotor 110 to a foundation 180, for example the floor of a building or adeck onboard a marine vessel. Fixture 120 is substantially rigidlycoupled to foundation 180 and therefore moves with foundation 180 whenfoundation 180 moves. Foundation 180 may undergo movement in a varietyof directions, for example horizontal translation as indicated by arrow152, vertical translation as indicated by arrows 154, and rotation asindicated by 150, or a combination thereof. Fixture 120 may form part ofa housing around rotor 110, such as a vacuum enclosure. In one example,the weight of rotor 110 is between 10 and 10,000 kilograms.

FIG. 2 illustrates one flywheel system 200 that includes an activemagnetic bearing to actively stabilize the rotor of the flywheel systemrelative to the foundation of the flywheel system. Flywheel system 200is an embodiment of flywheel system 100 that further includes an activemagnetic bearing 210 that utilizes magnetic coupling between rotor 110and fixture 120 to stabilize rotor 110 relative to fixture 120. Activemagnetic bearing 210 includes electromagnets to actively adjust theposition of rotor 110 relative to fixture 120. Active magnetic bearing210 may serve to maintain minimal or no friction during rotation ofrotor 110 about rotation axis 190 and/or prevent damage to flywheelsystem 200 associated with excessive physical contact between rotor 110and fixture 120. In one example, active magnetic bearing 210 ensuresthat the direction of rotation axis 190 remains sufficiently constantrelative to fixture 120 to ensure satisfactory performance of flywheelsystem 200 and to prevent damage to flywheel system 200.

FIG. 3 is a block diagram that schematically illustrates one activemagnetic bearing module 300 for a flywheel system such as flywheelsystem 200. Active magnetic bearing module 300 is an embodiment ofactive magnetic bearing 210. Active magnetic bearing module 300 includesa plurality of magnetizable elements 310 and a plurality ofelectromagnets 320 configured to magnetically couple with magnetizableelements 310 as shown schematically by arrows 330. Each magnetizableelement 310 may be a soft magnetic composite, a stack of laminatedtransformer steel, a stack of non-oriented electrical steel, or amagnetic material with intrinsic coercivity less than 1000 Ampere/meter.When active magnetic bearing module 300 is implemented in flywheelsystem 200, magnetizable elements 310 are mechanically coupled to rotor110 or integrated in rotor 110, and electromagnets 320 are mechanicallycoupled to fixture 120. Electromagnets 320 enable active adjustment ofthe position of rotor 110 relative to fixture 120.

In an embodiment, active magnetic bearing module 300 further includesone or more sensors 340 and at least one power supply 350. In operation,sensor(s) 340 senses a property of the position or motion of rotor 110relative to fixture 120 and communicates this property to power supply350 which controls the current passing through one or more ofelectromagnets 320 according to the property.

Active magnetic bearing module 300 cooperates with rotor 110 and fixture120 to form an embodiment of flywheel system 200.

FIG. 4 illustrates one active magnetic bearing 400 for use in a flywheelsystem. Active magnetic bearing 400 is an embodiment of magnetizableelements 310 and electromagnets 320 and may be implemented in flywheelsystem 200. Active magnetic bearing 400 includes (a) a plurality ofmagnetizable elements 410 arranged along a diameter 412 and (b) aplurality of electromagnets 420 arranged along a diameter 422 that issmaller than diameter 412 such that electromagnets 420 may be positionedwithin the ring of magnetizable elements 410. The number of magnetizableelements 410 and electromagnets 420 may be different from that shown inFIG. 4 , without departing from the scope hereof. Also without departingfrom the scope hereof, the number of magnetizable elements 410 may bedifferent from the number of electromagnets 420.

In one implementation of active magnetic bearing 400 in flywheel system200, each of diameters 412 and 422 is centered about rotation axis 190,as illustrated.

FIG. 5 illustrates one flywheel system 500 having an active magneticbearing 530 positioned in a void of the rotor. Flywheel system 500 is anembodiment of flywheel system 200, and active magnetic bearing 530 is anembodiment of active magnetic bearing 400. Flywheel system 500 includesa rotor 510 and a fixture 520. Rotor 510 forms a void 512. Void 512faces fixture 520 and encircles rotation axis 190. Void 512 may, butdoes not need to, span across rotation axis 190. A tip 514 extends fromrotor 510 toward fixture 520. Without departing from the scope hereof,tip 514 may be omitted from flywheel system 500.

Active magnetic bearing 530 includes a plurality of magnetizableelements 532 mechanically coupled to, or integrated in, rotor 510 at asurface 516 of void 512 facing rotation axis 190. Active magneticbearing 530 further includes a plurality of electromagnets 534mechanically coupled to fixture 520 via a mount 522. Mount 522 may forma hollow 523 that accommodates tip 514. In embodiments that do notinclude tip 514, mount 522 may be solid across rotation axis 190.Electromagnets 534 are configured to magnetically couple withmagnetizable elements 532 across the portion of void 512 betweenelectromagnets 534 and magnetizable elements 532. The nominal radial gap535 between magnetizable elements 532 and electromagnets 534, when rotor510 is radially centered about mount 522, may be in the range between 2and 10 millimeters. In operation, electromagnets 534 exert forces 538 onmagnetizable elements 532 at surface 516 to actively stabilize rotor 510relative to fixture 520.

The axial extent (along rotation axis 190) of magnetizable elements 532may exceed the axial extent of electromagnets 534, such that themagnetic coupling between magnetizable elements 532 and electromagnets534 is the same or similar even in the presence of axial movement ofrotor 510 relative to fixture 520. In one implementation, the axialextent of magnetizable elements 532 exceed the axial extent ofelectromagnets 534 by 10% in both axial directions.

In an embodiment, active magnetic bearing 530 includes one or moresensors 536 that senses a property of the position and/or motion ofrotor 510 relative to fixture 520. Sensor(s) 536 form an embodiment ofsensor(s) 340. Flywheel system 500 may further include power supply 350as discussed above in reference to FIG. 3 .

Fixture 520 may be positioned below a bottom end of rotor 510 (as shownin FIG. 5 ) or above a top end of rotor 510. Herein, the “bottom end”and “top end” of a rotor refer to the bottom end and top end,respectively, of the rotor when the rotation axis is vertical. It isunderstood that a flywheel system may be oriented with a non-verticalrotation axis, for example prior to installation in an operatingenvironment, or when the operating environment causes the orientation ofa nominally vertical rotation axis to deviate from vertical (e.g.,during movement and/or oscillation of the foundation supporting aflywheel system designed to operate with a generally verticalorientation axis). Similarly, the terms “above” and “below”, as usedherein, are referenced to the rotation axis. Fixture 520 is, forexample, an endplate of a housing around rotor 510. In certainembodiments, fixture 520 is a base of flywheel system 500. In suchembodiments, flywheel system 500 may further include a plurality ofpermanent magnets 540 mechanically coupled to rotor 510 and a pluralityof permanent magnets 542 mechanically coupled to fixture 520. Permanentmagnets 540 and 542 are configured to magnetically couple with eachother to bear the load of rotor 510 so as to magnetically levitate rotor510 above the base formed by fixture 520.

Without departing from the scope hereof, active magnetic bearing 530 maybe provided as a standalone bearing to be implemented in a third partyflywheel system. Active magnetic bearing 530 may be provided togetherwith one or more of power supply 350, permanent magnets 540, andpermanent magnets 542.

FIG. 6 illustrates an alternate flywheel system 600 implementing anactive magnetic bearing at a shaft of the flywheel system. Flywheelsystem 600 includes a rotor 610, a shaft 612 attached to rotor 610 (orintegrally formed therewith), and a base 620 positioned below a bottomend of rotor 610. Flywheel system 600 further includes (a) magnetizableelements 632 attached to shaft 612 and (b) electromagnets 634 extendingup from base 620 to magnetically couple with magnetizable elements 632on shaft 612. When utilizing electromagnets 634 to stabilize rotor 610relative to base 620, electromagnets 634 exert forces 638 inward onshaft 612. These forces concentrate significant stress on the area 614where shaft 612 and rotor 610 connect to each other.

In contrast, forces 538 in flywheel system 500 are directed outward ontoa larger surface of rotor 510 and do not generate the stress caused byforces 638 in flywheel system 600. The configuration of flywheel system500 thereby reduces or eliminates any adverse effect of active magneticbearing 530 on the performance and lifetime of flywheel system 500.

FIG. 7 illustrates one flywheel system 700 having an active magneticbearing that is integrated with a generator of the flywheel system.Flywheel system 700 is an embodiment of flywheel system 500. Flywheelsystem 700 includes a rotor 710 and fixture 520. Rotor 710 forms a void712. A portion of void 712 closer to fixture 520 has diameter 788, and aportion of void 712 farther from fixture 520 has diameter 786. Flywheelsystem 700 includes (a) a plurality of permanent magnets 742mechanically coupled to, or integrated in, rotor 710 at a surface 718 ofvoid 712 characterized by diameter 788, and (b) a generator stator 740mounted to fixture 520. Generator stator 740 includes a plurality ofwindings 744 that magnetically couple with permanent magnets 742 toconvert between rotational energy of rotor 710 and electrical energy inwindings 744. Generator stator 740 may function in both “generator mode”and “motor mode”. In “generator mode”, generator stator 740 deceleratesthe rotation of rotor 710 to generate electrical energy, in the form ofelectrical energy in windings 744, from rotational energy of rotor 710.In “motor mode”, generator stator 740 uses electrical energy, suppliedfrom an external source to windings 744, to accelerate the rotation ofrotor 710 and thereby increase the rotational energy of rotor 710. Inone implementation, windings 744 are water cooled, air cooled by forcedair, or passively air cooled. Flywheel system 700 further includesactive magnetic bearing 530 positioned in void 712. Flywheel system 700implements magnetizable elements 532 at a surface 716 of void 712characterized by diameter 786. Flywheel system 700 implementselectromagnets 534, and optionally sensor(s) 536 in a mount 722 abovegenerator stator 740.

A pair of tips 714 and 715 extend from rotor 710 toward fixture 520.Mount 722 and generator stator 740 may form respective hollows 723 and743 to accommodate tips 714 and 715. Without departing from the scopehereof, tips 714 and 715 may be omitted from flywheel system 700.

Fixture 520 may be positioned below a bottom end of rotor 710 (as shownin FIG. 7 ) or above a top end of rotor 710. Fixture 520 is, forexample, an endplate of a housing around rotor 710. In certainembodiments, fixture 520 is a base of flywheel system 700. In suchembodiments, flywheel system 700 may further include permanent magnets540 mechanically coupled to rotor 710 and permanent magnets 542mechanically coupled to fixture 520, to magnetically levitate rotor 710above the base formed by fixture 520.

In an embodiment, flywheel system 700 further includes a sensor array750 positioned in fixture 520 or mechanically coupled to fixture 520.Sensor array 750 senses motion properties of fixture 520 and may serveto impose limitations on the operation of flywheel system 700 accordingto such motion properties. For example, the rate of acceleration and/ordeceleration of rotor 710 may be limited during time periods whenfixture 520 undergoes relatively large movement.

The nominal radial gap 735 (when rotor 710 is radially centered abovegenerator stator 740 and mount 722) between magnetizable elements 532and electromagnets 534 may be smaller than the nominal radial gap 745between permanent magnets 742 and generator stator 740, so as to provideactive stabilization with sufficient accuracy to ensure that permanentmagnets 742 do not come into physical contact with any portion ofgenerator stator 740. In one example, nominal radial gap 745 is at leasttwice the value of nominal radial gap 735. Nominal radial gap 735 may besimilar to nominal radial gap 535.

Without departing from the scope hereof, diameters 786 and 788 may beidentical such that surfaces 716 and 718 are respective portions of acommon cylindrical surface.

Also without departing from the scope hereof, active magnetic bearing530 and generator stator 740 may be provided as a standalone integratedbearing module to be implemented in a third party flywheel system. Thisintegrated bearing module may further include one or more of mount 722,power supply 350, permanent magnets 540, and permanent magnets 542.

FIG. 8 illustrates one bearing module 800 having both an active magneticbearing and a passive magnetic backup bearing. Bearing module 800 is anextension of active magnetic bearing module 300 that further includespermanent magnets 810 mechanically coupled to rotor 110 and permanentmagnets 820 mechanically coupled to fixture 520. Permanent magnets 810and 820 are configured to magnetically couple with each other (asindicated by magnetic coupling 830). In the event that electromagnets320 should be incapable of sufficiently stabilizing rotor 110 relativeto fixture 120, for example if power supply 350 fails, permanent magnets810 and 820 form a passive magnetic bearing configured to provide atleast some degree of stabilization of rotor 110 relative to fixture 120.The backup stabilization provided by permanent magnets 810 and 820 maybe sufficient to prevent catastrophic damage of a flywheel systemimplementing bearing module 800 and, for example, safely stabilize rotor110 during deceleration to a standstill.

FIG. 9 illustrates one exemplary flywheel system 900 that has an activemagnetic bearing integrated with a generator of the flywheel system andfurther includes one or more passive magnetic backup bearings. Flywheelsystem 900 is an embodiment of flywheel system 700 that further includesone or more passive backup bearings 910. Each bearing 910 includespermanent magnets 810 and 820 respectively coupled to rotor 710 andfixture 520 (directly or indirectly). FIG. 9 shows several exemplarylocations of bearings 910. In embodiments including multiple bearings910, smaller and/or less powerful permanent magnets 810 and 820 maysuffice to achieve the same backup magnetic force as in embodimentsutilizing a single, more powerful bearing 910. Without departing fromthe scope hereof, flywheel system 900 may include more or fewer bearings910 than shown in FIG. 9 , and bearing(s) 910 may be located inposition(s) different from those shown in FIG. 9 . Also withoutdeparting from the scope hereof, one or more bearings 910 may beimplemented in flywheel system 500.

Also without departing from the scope hereof, active magnetic bearing530, generator stator 740, and passive magnetic bearing(s) 910 may beprovided as a standalone integrated bearing module to be implemented ina third party flywheel system. This integrated bearing module mayfurther include one or more of mount 722, power supply 350, permanentmagnets 540, and permanent magnets 542.

FIG. 10 illustrates another flywheel system 1000 having an activemagnetic bearing that is integrated with a generator of the flywheelsystem. Flywheel system 1000 is similar to flywheel system 700 exceptthat, in flywheel system 700, generator stator 740 is closer than activemagnetic bearing 530 to fixture 520 whereas, in flywheel system 1000,generator stator 740 is farther than active magnetic bearing 530 fromfixture 520. In flywheel system 1000, generator stator 740 and permanentmagnets 742 are in the portion of void 712 associated with surface 716,and active magnetic bearing 530 is in the portion of void 712 associatedwith surface 718. In flywheel system 1000, electromagnets 534 aremechanically coupled to fixture 520 via a mount 1022 that is similar tomount 722.

Although not shown in FIG. 10 , it is understood that flywheel system1000 may further include one or more passive backup bearings 910 asdiscussed above in reference to FIG. 9 .

FIG. 11 illustrates one flywheel system 1100 having an active magneticbearing that is integrated with a generator of the flywheel system withboth the active magnetic bearing and the generator being mounted above atop end of the rotor of the flywheel system. Flywheel system 1100 issimilar to flywheel system 1000. However, as compared to flywheel system1000, rotor 710 is replaced by a rotor 1110 that is upside down relativeto rotor 710 such that void 712 faces upwards. Mount 1022 and generatorstator 740 are suspended from a top plate 1130 positioned above a topend of rotor 1110. In flywheel system 1100, top plate 1130 and fixture520 may form respective endplates of a housing that encloses rotor 1110.It is understood that each of flywheel systems 700 and 900 may bemodified in a similar manner with bearings and generator stator beingsuspended from above.

FIG. 12 illustrates one flywheel system 1200 including generator stator740 and an active magnetic bearing 1230 positioned at greater radii thangenerator stator 740. Flywheel system 1200 is an embodiment of flywheelsystem 500. Flywheel system 1200 includes fixture 520 and a rotor 1210.Rotor 1210 forms (a) a groove 1232 encircling rotation axis 190 andhaving an inner diameter 1286 and (b) a central void 1212 that issimilar to void 512 and has a diameter 1282 which is smaller than innerdiameter 1286. A tip 1214 extends from rotor 1210 toward fixture 520inside void 1212. Void 1212 accommodates generator stator 740 which mayform a hollow for accommodating tip 1214. Without departing from thescope hereof, tip 1214 may be omitted from flywheel system 1200.

Flywheel system 1200 further includes permanent magnets 742 positionedat a surface 1216 of void 1212. Windings 744 of generator stator 740magnetically couple with permanent magnets 742 as discussed above inreference to FIG. 7 . Groove 1232 accommodates electromagnets 534mechanically coupled to fixture 520 and configured to magneticallycouple with magnetizable elements 532 across a portion of groove 1232.Groove 1232 may further accommodate sensor(s) 536. Magnetizable elements532 are mechanically coupled to, or integrated in, rotor 1210 andarranged along a diameter that is smaller than the diameter associatedwith electromagnets 534. In flywheel system 1200, magnetizable elements532 and electromagnets 534 cooperate to form an active magnetic bearingmagnetic.

Flywheel system 1200 may include one or more passive backup bearings910. FIG. 12 shows exemplary locations of such bearings 910.Alternatively, one or more passive backup bearings 910 may be positionedat least partly in groove 1232. In an embodiment, flywheel system 1200includes permanent magnets 540 and 542 configured as discussed above inreference to FIG. 5 .

Without departing from the scope hereof, rotor 1210 may be turned upsidedown in a manner similar to that discussed for rotor 1110 in referenceto FIG. 11 .

Also without departing from the scope hereof, active magnetic bearing1230 and generator stator 740, and optionally passive magneticbearing(s) 910, may be provided as a standalone integrated bearingmodule to be implemented in a third party flywheel system. Thisintegrated bearing module may further include one or more of powersupply 350, permanent magnets 540, and permanent magnets 542.

FIG. 13 illustrates one flywheel system 1300 including generator stator740, permanent magnets 742, and an active magnetic bearing 1330positioned at greater radii than generator stator 740 and permanentmagnets 742. Flywheel system 1300 is similar to flywheel system 1200except that active magnetic bearing 1230 is replaced by active magneticbearing 1330. Active magnetic bearing 1330 is similar to active magneticbearing 1230 except that, in active magnetic bearing 1330, magnetizableelements 532 are disposed farther than electromagnets 534 from rotationaxis 190.

Combinations of Features

Features described above as well as those claimed below may be combinedin various ways without departing from the scope hereof. For example, itwill be appreciated that aspects of one flywheel system or bearingmodule described herein may incorporate or swap features of anotherflywheel system or bearing module described herein. The followingexamples illustrate possible, non-limiting combinations of embodimentsdescribed above. It should be clear that many other changes andmodifications may be made to the methods and device herein withoutdeparting from the spirit and scope of this invention:

(A1) A flywheel system may include a rotor configured to rotate about arotation axis, a fixture, and a bearing module for at least one of (a)supporting the rotor on the fixture and (b) stabilizing the rotorrelative to the fixture.

(A2) In the flywheel system denoted as (A1), the bearing module mayinclude an active magnetic bearing for actively stabilizing the rotorrelative to the fixture.

(A3) In the flywheel system denoted as (A2), the active magnetic bearingmay include a plurality of first magnetizable elements mechanicallycoupled to or integrated in the rotor, and a plurality of electromagnetsmechanically coupled to the fixture and configured to magneticallycouple with the plurality of first magnetizable elements to activelystabilize the rotor relative to the fixture.

(A4) In the flywheel system denoted as (A3), each of the firstmagnetizable elements may be a soft magnetic composite.

(A5) In either of the flywheel systems denoted as (A3) and (A4), each ofthe first magnetizable elements may be farther than each of theelectromagnets from the rotation axis.

(A6) In any of the flywheel systems denoted as (A3) through (A5), thefirst magnetizable elements may be arranged along a first diameter aboutthe rotation axis, and the electromagnets being arranged along a seconddiameter about the rotation axis, wherein the first diameter is greaterthan the second diameter.

(A7) In any of the flywheel systems denoted as (A3) through (A6), indimensions orthogonal to the rotation axis, the electromagnets and thefirst magnetizable elements may be away from each other by a firstradial gap, the first radial gap being in range between 2 and 10millimeters

(A8) In any of the flywheel systems denoted as (A3) through (A7), therotor may form a first void encircling the rotation axis, and theplurality of first magnetizable elements may be positioned at a firstsurface of the first void that encircles the rotation axis and faces orfaces away from the rotation axis.

(A9) In the flywheel system denoted as (A8), each of the firstmagnetizable elements may extend along a portion of the rotation axis.

(A10) In either of the flywheel systems denoted as (A8) and (A9), eachof the electromagnets may be positioned in the first void tomagnetically couple with the first magnetizable elements across aportion of the first void.

(A11) The flywheel system denoted as (A10) may further include (i)permanent magnets mechanically coupled to or integrated in the rotor andpositioned at a second surface of the first void that encircles therotation axis, and (ii) a generator stator mechanically coupled to thefixture and positioned in the first void to magnetically couple with thepermanent magnets, so as to convert between rotational energy of therotor and electric current in windings of the generator stator.

(A12) In the flywheel system denoted as (A11), the fixture may includean endplate positioned adjacent a top end or bottom end of the rotor,and the electromagnets and the generator stator may be attached to theendplate.

(A13) In the flywheel system denoted as (A12), the generator stator maybe between the electromagnets and the endplate, and the second surfacemay be closer than the first surface to the endplate.

(A14) In the flywheel system denoted as (A12), the electromagnets may bebetween the generator stator and the endplate, and the first surfacebeing closer than the second surface to the endplate.

(A15) In any of the flywheel systems denoted as (A12) through (A14), theendplate may form a base adjacent the bottom-end, and the flywheelsystem may further include (I) first load bearing magnets mechanicallycoupled to or integrated in the rotor at bottom surface of rotor, and(II) second load bearing magnets, mechanically coupled to the base, formagnetically coupling with the first load bearing magnets tomagnetically levitate the rotor above the base.

(A16) Any of the flywheel systems denoted as (A12) through (A15) mayfurther include, in the first void, at least one passive magneticbearing for stabilizing the rotor relative to the fixture if the activemagnetic bearing loses power.

(A17) In the flywheel system denoted as (A16), the at least one passivemagnetic bearing may include a plurality of passive magnetic bearingslocated in different respective positions.

(A18) In the flywheel system denoted as (A16), each passive magneticbearing may include second permanent magnets mechanically coupled to orintegrated in the rotor, and third permanent magnets mechanicallycoupled to the fixture and positioned in the first void to magneticallycouple with the second permanent magnets, so as to provide backupstabilization of the rotor relative to the fixture.

(A19) In any of the flywheel systems denoted as (A11) through (A12),each of the first surface and the second surface may face the rotationaxis.

(A20) In the flywheel system denoted as (A19), the first surface and thesecond surface may be respective portions of a common cylindricalsurface.

(A21) In the flywheel system denoted as (A19), diameter of the firstsurface may be different from diameter of the second surface.

(A22) In any of the flywheel systems denoted as (A19) through (A21), thefirst void may span across the rotation axis.

(A23) In the flywheel system denoted as (A10), the first void may be agroove that encircles the rotation axis but does not coincide with therotation axis.

(A24) In the flywheel system denoted as (A23), the first surface mayface away from the rotation axis, such that the first magnetizableelements are closer than the electromagnets to the rotation axis.

(A25) In either of the flywheel systems denoted as (A23) and (A24), therotor may further form a central void closer than the groove to therotation axis, and the flywheel system may further include permanentmagnets mechanically coupled to or integrated in the rotor andpositioned at a second surface of the central void that faces andencircles the rotation axis, and a generator stator mechanically coupledto the fixture and positioned in the central void to magnetically couplewith the permanent magnets, so as to convert between rotational energyof the rotor and electric current in windings of the generator stator.

(A26) In the flywheel system denoted as (A25), the fixture may includean endplate positioned adjacent a top end or bottom end of the rotor,and the electromagnets and the generator stator may be attached to theendplate.

(A27) In the flywheel system denoted as (A26), the endplate may form abase positioned adjacent a bottom end of the rotor, and the flywheelsystem may further include (I) first load bearing magnets mechanicallycoupled to or integrated in the rotor at bottom surface of rotor, and(II) second load bearing magnets, mechanically coupled to the base, formagnetically coupling with the first load bearing magnets tomagnetically levitate the rotor above the base.

(A28) Any of the flywheel systems denoted as (A25) through (A27) mayfurther include, in one or both of the groove and the central void, atleast one passive magnetic bearing for stabilizing the rotor relative tothe fixture if the active magnetic bearing loses power.

(A29) In the flywheel system denoted as (A28), the at least one passivemagnetic bearing may include a plurality of passive magnetic bearingslocated in different respective positions.

(A30) In either of the flywheel systems denoted as (A28) and (A29), eachpassive magnetic bearing may include second permanent magnetsmechanically coupled to or integrated in the rotor, and third permanentmagnets mechanically coupled to the fixture and positioned in the grooveor the central void to magnetically couple with the second permanentmagnets, so as to provide backup stabilization of the rotor relative tothe fixture.

(A31) Any of the flywheel systems denoted as (A3) through (A30) mayfurther include a power supply for powering the plurality ofelectromagnets to adjust position of the rotor relative to the fixture.

(A32) The flywheel system denoted as (A31) may further include at leastone sensor for sensing a movement characteristic of the rotor relativeto the fixture, wherein the at least one sensor is communicativelycoupled with the power supply to enable adjustment of the position ofthe rotor relative to the fixture in response to the movementcharacteristic

(A33) The flywheel system denoted as (A32) may further include at leastone passive backup bearing that includes second permanent magnets forstabilizing the rotor relative to the fixture if the power supply failsto provide power to the one or more electromagnets.

(B1) A bearing module for a flywheel system may include a plurality offirst magnetizable elements arranged along a first diameter andconfigured to be mechanically coupled to a rotor of the flywheel system,and a plurality of electromagnets configured to be mechanically coupledto a fixture and magnetically couple with the first magnetizableelements to stabilize the rotor relative to the fixture, wherein theelectromagnets are bounded by a second diameter that is smaller than thefirst diameter to enable positioning of the electromagnets inside thefirst diameter.

(B2) In the bearing module denoted as (B1), each of the firstmagnetizable elements may be a soft magnet.

(B3) Either of the bearing modules denoted as (B1) and (B2) may furtherinclude at least one sensor for sensing a position characteristic of therotor relative to the fixture, and a power supply, communicativelycoupled with the at least one sensor, for powering the electromagnets toadjust position of the rotor relative to the fixture in response to theposition characteristic.

(B4) Any of the bearing modules denoted as (B1) through (B3) may furtherinclude at least one passive magnetic bearing including (a) a pluralityof first permanent magnets configured to be mechanically coupled to therotor and (b) a plurality of second permanent magnets configured to bemechanically coupled to the fixture and magnetically couple with thefirst permanent magnets to stabilize the rotor relative to the fixtureif the power supply fails to provide power to the electromagnets.

(B5) Any of the bearing modules denoted as (B1) through (B4) may furtherinclude a plurality of third permanent magnets arranged along a thirddiameter and configured to be mechanically coupled to the rotor, and agenerator stator for magnetically coupling with the third permanentmagnets, to convert between rotational energy of the rotor and electriccurrent in windings of the generator stator.

(B6) In the bearing module denoted as (B5), the generator stator may bebounded by a fourth diameter that is smaller than the third diameter toenable positioning of the generator stator inside the third diameter.

(B7) In the bearing module denoted as (B6), the electromagnets may bemounted on the generator stator.

(B8) Any of the bearing modules denoted as (B1) through (B7) may furtherinclude first load bearing magnets configured to be mechanically coupledto the rotor, and second load bearing magnets configured to bemechanically coupled to the fixture and magnetically couple with thefirst load bearing magnets to magnetically levitate the rotor above thesecond load bearing magnets.

(C1) A bearing module integrated with a generator for use in a flywheelsystem may include (1) a plurality of permanent magnets arranged along afirst diameter and configured to be mechanically coupled to a rotor ofthe flywheel system, (2) a generator stator configured to bemechanically coupled to a fixture, the generator stator being bounded bya second diameter that is smaller than the first diameter to enablepositioning of the generator stator inside the first diameter tomagnetically couple with the permanent magnets, so as to convert betweenrotational energy of the rotor and electric current in windings of thegenerator stator, and (3) an active magnetic bearing including (a) aplurality of first magnetizable elements arranged along a third diameterand configured to be mechanically coupled to the rotor, wherein thethird diameter is greater than the first diameter to enable positioningof the first magnetizable elements at greater distance than thepermanent magnets from rotation axis of the rotor, and (b) a pluralityof electromagnets arranged along a fourth diameter and configured to bemechanically coupled to the fixture and magnetically couple with thefirst magnetizable elements, so as to actively stabilize the rotorrelative to the fixture, wherein the fourth diameter is greater than thefirst diameter to enable positioning of the active magnetic bearing atgreater distance than the permanent magnets from the rotation axis.

(C2) In the bearing module denoted as (C1), each of the firstmagnetizable elements may be a soft magnet.

(C3) In either of the bearing modules denoted as (C1) and (C2), thefourth diameter may be greater than the third diameter to enablepositioning of the first magnetizable elements closer than theelectromagnets to the rotation axis.

(C4) In either of the bearing modules denoted as (C1) and (C2), thefourth diameter may be smaller than the third diameter to enablepositioning of the first magnetizable elements farther than theelectromagnets from the rotation axis.

(C5) Any of the bearing modules denoted as (C1) through (C4) may furtherinclude an endplate that forms at least a portion of the fixture, andthe generator stator and the electromagnets may be mounted on theendplate.

(C6) Any of the bearing modules denoted as (C1) through (C5) may furtherinclude first load bearing magnets configured to be mechanically coupledto the rotor, and second load bearing magnets configured to bemechanically coupled to the fixture and magnetically couple with thefirst load bearing magnets to magnetically levitate the rotor above thesecond load bearing magnets.

(C7) Any of the bearing module denoted as (C1) through (C6) may furtherinclude at least one sensor for sensing a position characteristic of therotor relative to the fixture, and a power supply, communicativelycoupled with the at least one sensor, for powering the electromagnets toadjust position of the rotor relative to the fixture in response to theposition characteristic.

(C8) Any of the bearing modules denoted as (C1) through (C7) may furtherinclude at least one passive magnetic bearing including (a) a pluralityof second permanent magnets configured to be mechanically coupled to therotor and (b) a plurality of third permanent magnets configured to bemechanically coupled to the fixture and magnetically couple with thesecond permanent magnets to stabilize the rotor relative to the fixtureif the power supply fails to provide power to the electromagnets.

Changes may be made in the above systems and methods without departingfrom the scope hereof. It should thus be noted that the matter containedin the above description and shown in the accompanying drawings shouldbe interpreted as illustrative and not in a limiting sense. Thefollowing claims are intended to cover generic and specific featuresdescribed herein, as well as all statements of the scope of the presentsystems and methods, which, as a matter of language, might be said tofall therebetween.

What is claimed is:
 1. A flywheel system comprising: a fixture providinga base and a stator; a rotor having a cavity for receiving the stator; agenerator/motor module comprising a plurality of permanent magnetsmechanically coupled to the rotor and magnetically coupled to windingsof the stator, wherein the generator/motor module is configured toconvert between rotational energy of rotor and electrical energy inwindings of the stator; an active magnetic bearing module for activelystabilizing the rotor relative to the fixture, the active magneticbearing module comprising: a plurality of magnetizable elementsmechanically coupled with the rotor, and a plurality of electromagnetsmechanically coupled to a shaft and configured to magnetically couplewith the plurality of magnetizable elements to actively stabilize therotor relative to the shaft; wherein the windings of the generator/motormodule are arranged around a rotation axis of the rotor at a firstdistance from the rotation axis of the rotor; wherein the electromagnetsof the active magnetic bearing module are arranged around the rotationaxis of the rotor at a second distance from the rotation axis of therotor; and wherein the first distance is greater than or equal to thesecond distance.
 2. The flywheel system according to claim 1, furthercomprising a levitation module configured to magnetically levitate therotor above the base.
 3. The flywheel system according to claim 2,wherein the levitation module comprises: a first set of permanentmagnets mechanically coupled to the stator, and a second set ofpermanent magnets mechanically coupled to the rotor; wherein the firstand the second set of permanent magnets are configured to magneticallycouple with each other to bear the load of the rotor to magneticallylevitate the rotor above the base.
 4. The flywheel system according toclaim 3, wherein the stator is provided as a shaft for the rotor; thefirst and the second set of permanent magnets are configured tomagnetically couple with each other in an axial direction of the shaft.5. The flywheel system according to claim 1, wherein the rotor has avertical rotation axis, wherein the base of the fixture is formed as ahorizontal endplate for the rotor.
 6. The flywheel system according toclaim 1, wherein the generator/motor module and the active magneticbearing module are arranged around the shaft at different distances tothe base.
 7. The flywheel system according to claim 1, wherein thegenerator/motor module is configured to operate in a generator mode andin a motor mode; wherein in the generator mode, the generator stator isused to decelerate the rotation of rotor to generate electrical energy,in the form of electrical energy in the windings; wherein in the motormode, the generator stator uses electrical energy, supplied from anexternal source to the windings to accelerate the rotation of rotor andthereby increase the rotational energy of rotor.
 8. The flywheel systemaccording to claim 7, wherein the generator stator is configured forcooling the windings during operation.
 9. The flywheel system accordingto claim 1, wherein the active magnetic bearing module is connected to apower supply for powering the plurality of electromagnets to adjustposition of the rotor relative to the fixture, and at least one sensoris configured for sensing a movement characteristic of the rotorrelative to the fixture; the at least one sensor being communicativelycoupled with the power supply to enable adjustment of the position ofthe rotor relative to the fixture in response to the movementcharacteristic.
 10. The flywheel system according to claim 1, whereinthe active magnetic bearing module is connected to a power supply forpowering the plurality of electromagnets to adjust position of the rotorrelative to the fixture; the at least one sensor is configured forsensing a position characteristic of the rotor relative to the fixture,the at least one sensor being communicatively coupled with the powersupply for powering the electromagnets to adjust position of the rotorrelative to the fixture in response to the position characteristic. 11.The flywheel system according to claim 1, wherein the magnetic bearingmodule further includes one or more sensors and at least one powersupply; the one or more sensors senses a property of the position ormotion of rotor relative to fixture and communicates this property tothe power supply for controlling the current passing through theplurality of electromagnets.
 12. The flywheel system according to claim1, further comprising a sensor array coupled to the fixture; the sensorarray being configured for sensing motion properties of the fixture; theflywheel system is configured to impose limitations on the operation offlywheel system according to the sensed motion properties.
 13. Theflywheel system according to claim 12, wherein the imposed limitationson the operation of flywheel system includes limitation of at least oneof (i) a rate of acceleration and (ii) a rate of deceleration of rotorduring periods when fixture undergoes movement above a predefinedthreshold.
 14. The flywheel system according to claim 1, wherein theplurality of magnetizable elements exceed an axial extent of theplurality of electromagnets of the active magnetic bearing module, suchthat the magnetic coupling between the plurality of magnetizableelements and the plurality of electromagnets remains stable in thepresence of axial movement of rotor relative to fixture.
 15. Theflywheel system according to claim 14, wherein the axial extent ofmagnetizable elements exceed the axial extent of electromagnets by 10%in both axial directions.
 16. The flywheel system according to claim 1,wherein the active magnetic bearing module in an axial direction of thestator is arranged in between the generator/motor module and the base ofthe fixture.
 17. The flywheel system according to claim 16, wherein thecavity of the rotor is configured at the generator/motor module as afirst cylinder surface having a first diameter, and at the activemagnetic bearing module as a second cylinder surface having a seconddiameter, and wherein second diameter is larger or equals the firstdiameter.
 18. The flywheel system according to claim 17, wherein thefirst diameter and the second diameter are identical such that firstcylinder surface and the second cylinder surface are respective portionsof a common cylindrical surface.
 19. The flywheel system according toclaim 1, wherein the plurality of magnetizable elements of the activemagnetic bearing module and mechanically coupled with the rotor arearranged at a first diameter and the plurality of electromagnets of theactive magnetic bearing module and mechanically coupled to the shaft arearranged at a second diameter, the first diameter being greater than thesecond diameter.
 20. A flywheel system comprising: a fixture providing abase and a stator; a rotor having a cavity for receiving the stator; agenerator/motor module comprising a plurality of permanent magnetsmechanically coupled to the rotor and magnetically coupled to windingsof the stator, wherein the generator/motor module is configured toconvert between rotational energy of rotor and electrical energy inwindings of the stator; an active magnetic bearing module for activelystabilizing the rotor relative to the fixture, the active magneticbearing module comprising: a plurality of magnetizable elementsmechanically coupled with the rotor, and a plurality of electromagnetsmechanically coupled to a shaft and configured to magnetically couplewith the plurality of magnetizable elements to actively stabilize therotor relative to the shaft; wherein the electromagnets of the activemagnetic bearing module are arranged as a first ring around a rotationaxis of the rotor; wherein the magnetizable elements of the activemagnetic bearing module are arranged as a second ring around therotation axis of the rotor; and wherein the first and second rings arearranged as concentric rings in a plane parallel to the base of thefixture, the first and second rings are configured as an inner ring andan outer ring, respectively.